In most cases, a genetic etiology of CVID is not identified; however, there are several monogenic IEI with CVID phenotypes, including genes encoding for the BCR complex (CD19, CD21, and CD81), NFκB-associated defects, or the BAFF receptors (TACI and BAFF-R), which confer an increased risk of CVID. Here, TNFRSF13C is linked to common variable immunodeficiency.